Autofocus technology: Active Triangulation
Autofocus technology: Active Triangulation | ||
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Active triangulation— unlike timing autofocus, which uses the same transducer to generate and receive bursts of light—works with one device to shine an infrared beam of light at the photo's subject and a second device to receive the light after it bounces off the subject. The separate devices allow the autofocus mechanism to make use of the different angles formed by the light's path to the subject and its path on the return trip. An object far away from the camera reflects the light at a smaller angle than an object closer to the camera. When the returning light enters a window in the camera, a mask prevents the light from reaching a strip of light-sensitive material. The mask is linked to the lens's focusing mechanism. As a motor turns the lens, the mask moves across the strip. When a slot in the mask reaches the returning beam of light, the slot allows the light to strike the light-sensitive strip. In the case of a spring-powered mechanism, the strip generates an electrical current that energizes an electromagnet, which stops the motion of the lens at the point at which the lens revolves into focus. In a motor-assisted lens, the current switches off the motor. | ||